Liquid-crystal display device

ABSTRACT

Disclosed is a liquid-crystal display device comprising a polarizing plate comprising a polarizing element and a thermoplastic-resin film which comprises a lactone ring-having polymer and satisfies the following formulas (I) and (II): 
       0≦| Re (630)|≦10, and | Rth (630)|≦25  (I)
 
       | Re (400)− Re (700)|≦10, and | Rth (400)− Rth (700)|≦35  (II)
         wherein Re(λ) means retardation (nm) in plane at a wavelength λ nm; and Re(λ) means retardation (nm) along the thickness direction at a wavelength λ nm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/680,075,filed Mar. 25, 2010, which was the National Stage filing under §371 ofPCT/JP2008/067979, filed Sep. 26, 2008, which in turn claims priority toJapanese Application Nos. 2007-251971, filed Sep. 27, 2007, and2008-085530, filed Mar. 28, 2008, the entire contents of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a liquid-crystal display device, inparticular to a liquid-crystal display device, employing an in-planeswitching-mode, in which an electric field is applied to thehorizontally-aligned nematic liquid crystal laterally.

2. Related Art

An in-plane switching (IPS)-mode liquid-crystal display device has beenproposed in which a lateral electric field is applied to the liquidcrystal. Recently, the liquid-crystal display device employing the modehas been developed for use for TVs, and with that, the panel brightnessthereof has become greatly increased. Accordingly, even slight lightleakage in diagonal oblique directions in the black state, which hasheretofore been almost disregarded in IPS-mode devices, has becomeconsidered a cause of deterioration of display image quality in thedevices.

For improving the color expression of IPS-mode display devices and forimproving the viewing angle characteristics thereof in the black state,some methods of disposing an optical compensatory material havingbirefringent characteristics between the liquid-crystal layer and thepolarizer have been tried. And some methods of making a protective filmof the polarizer capable of functioning as an optical compensation havealso been tried for example, see JPA Nos. hei 9-80424, hei 10-54982, hei11-202323, hei 9-292522, hei 11-133408, hei 11-305217, hei 10-307291 and2006-227606.

SUMMARY OF THE INVENTION

However, even according to the methods proposed as in the above, theoptical characteristics (especially Rth) of the retardation film varydepending on the ambient temperature; and therefore there are problemsin that, depending on the condition for viewing them, the displaycharacteristics of liquid-crystal display devices may greatly vary andΔnd of the liquid-crystal cell in the devices may be noticeably uneven.Some retardation films suffers from increasing the absolute values oftheir optical characteristics (especially Re) depending on temperature-or humidity-change; and the increase in the absolute value of Re mayaugment the molecular axis fluctuation that a retardation filmnecessarily has, therefore causing a reason of lowering front contrastwhich means contrast in the normal line direction to the displayingplane.

The present invention has been made in consideration of theabove-mentioned various problems, and its object is to provide aliquid-crystal display device, in particular an IPS-mode liquid-crystaldisplay device, that is free from a problem of display performancefluctuation to be caused by temperature- or humidity-change.

Another object of the invention is to provide a liquid-crystal displaydevice, in particular an IPS-mode liquid-crystal display device, that isfree from problems of color shift in oblique directions and frontcontrast reduction to occur depending on the environment humidity andtemperature.

The means for achieving the above mentioned objects are as follows.

[1] A liquid-crystal display device comprising:

a liquid-crystal cell which comprises:

-   -   a pair of substrates disposed to face each other having an        electrode on at least one of them, the electrode capable of        forming an electric field containing a component running in        parallel to the substrate, and    -   a liquid-crystal layer, of which alignment is controlled,        disposed between the pair of substrates; and

a pair of polarizing plates disposed to sandwich the liquid-crystal celltherebetween,

wherein at least one of the pair of polarizing plates comprises apolarizing element and a thermoplastic-resin film which comprises alactone ring-having polymer and satisfies the following formulas (I) and(II):

0≦|Re(630)≦10, and |Rth(630)|≦25  (I)

|Re(400)−Re(700)|≦10, and |Rth(400)−Rth(700)|≦35  (II)

wherein Re(λ) means retardation (nm) in plane at a wavelength λ nm; andRe(λ) means retardation (nm) along the thickness direction at awavelength λ nm.

[2] The liquid-crystal display device as set forth in [1], wherein apolarizing plate disposed at the backlight side, at least, is saidpolarizing plate comprising the thermoplastic-resin film.[3] The liquid-crystal display device as set forth in [1], wherein apolarizing plate disposed at the displaying plane side, at least, issaid polarizing plate comprising the thermoplastic-resin film.[4] The liquid-crystal display device as set forth in [1], wherein bothof polarizing plates disposed at the backlight side and the displayingplane side are said polarizing plates comprising the thermoplastic-resinfilm.[5] The liquid-crystal display device as set forth in any one of [1] to[4], wherein Re{T} and Rth{T} (T means the temperature (° C.) at whichthe data is measured) of the thermoplastic-resin film at a wavelength of550 nm satisfy the following formulas (III) and (IV):

|Re{50}−Re{25}|<5,  (III)

|Rth{50}−Rth{25}|<10.  (IV)

[6] The liquid-crystal display device as set forth in any one of [1] to[5], wherein Re[H] and Rth[H] (H means the relative humidity (%) atwhich the data is measured) of the thermoplastic-resin film at awavelength of 550 nm satisfy the following formulas (V) and (VI):

|Re[80]−Re[10]|<5,  (V)

|Rth[80]−Rth[10]|<10.  (VI)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of one example of aliquid-crystal display device of the invention.

In the drawing, the reference numerals have the following meanings.

-   10 IPS-mode liquid-crystal cell-   12 a, 12 b Polarizing element-   14 a, 14 b Protective film on liquid-crystal cell side-   16 a, 16 b Outer protective film-   PLa Polarizing plate on panel side-   PLb Polarizing plate on back side

PREFERRED EMBODIMENT OF THE INVENTION

The invention is described in detail hereinunder.

In this description, the numerical range expressed by the wording “anumber to another number” means the range that falls between the formernumber indicating the lowermost limit of the range and the latter numberindicating the uppermost limit thereof.

In the description, Re(λ) and Rth(λ) each indicate retardation in plane(unit: nm) and retardation along thickness direction (unit: nm) at awavelength λ. Re(λ) is measured by applying a light having a wavelengthof λ nm in the normal line direction of a sample such as a film, usingKOBRA-21ADH or WR (by Oji Scientific Instruments).

When the sample to be tested is represented by an uniaxial or biaxialrefractive index ellipsoid, then its Rth(λ) is calculated according tothe method mentioned below.

With the in-plane slow axis (determined by KOBRA 21ADH or WR) taken asthe inclination axis (rotation axis) of the sample (in case where thesample has no slow axis, the rotation axis of the sample may be in anyin-plane direction of the sample), Re(λ) of the sample is measured at 6points in all thereof, up to +50° relative to the normal line directionof the sample at intervals of 10°, by applying a light having awavelength of λ nm from the inclined direction of the sample.

With the in-plane slow axis from the normal line direction taken as therotation axis thereof, when the sample has a zero retardation value at acertain inclination angle, then the symbol of the retardation value ofthe sample at an inclination angle larger than that inclination angle ischanged to a negative one, and then applied to KOBRA 21ADH or WR forcomputation.

With the slow axis taken as the inclination axis (rotation axis) (incase where the sample has no slow axis, the rotation axis of the samplemay be in any in-plane direction of the film), the retardation values ofthe sample are measured in any inclined two directions; and based on thedata and the mean refractive index and the inputted thickness of thesample, Rth may be calculated according to the following formulae (10)and (11):

$\begin{matrix}{{{Re}(\theta)} = {\lbrack {{nx} - \frac{{ny} \times {nz}}{\sqrt{\begin{matrix}{\{ {{ny}\; {\sin ( {\sin^{- 1}( \frac{\sin ( {- \theta} )}{nx} )} )}} \}^{2} +} \\\{ {{nz}\; {\cos ( {\sin^{- 1}( \frac{\sin ( {- \theta} )}{nx} )} )}} \}^{2}\end{matrix}}}} \rbrack \times \frac{d}{\cos \{ {\sin^{- 1}( \frac{\sin ( {- \theta} )}{nx} )} \}}}} & (10) \\{\mspace{79mu} {{Rth} = {\{ {{( {{nx} + {ny}} )/2} - {nz}} \} \times d}}} & (11)\end{matrix}$

wherein Re(θ) means the retardation value of the sample in the directioninclined by an angle θ from the normal line direction; nx means thein-plane refractive index of the sample in the slow axis direction; nymeans the in-plane refractive index of the sample in the directionvertical to nx; nz means the refractive index of the sample vertical tonx and ny; and d is a thickness of the sample.

When the sample to be tested can not be represented by a monoaxial orbiaxial index ellipsoid, or that is, when the sample does not have anoptical axis, then its Rth(λ) may be calculated according to the methodmentioned below.

With the in-plane slow axis (determined by KOBRA 21ADH or WR) taken asthe inclination axis (rotation axis) of the sample, Re(λ) of the sampleis measured at 11 points in all thereof, from −50° to +50° relative tothe normal line direction of the sample at intervals of 10°, by applyinga light having a wavelength of λ nm from the inclined direction of thesample. Based on the thus-determined retardation data of Re(λ), the meanrefractive index and the inputted thickness of the sample, Rth(λ) of thesample is calculated with KOBRA 21ADH or WR.

The mean refractive index may be used values described in catalogs forvarious types of optical films. When the mean refractive index has notknown, it may be measured with Abbe refractometer. The mean refractiveindex for major optical film is described below: cellulose acetate(1.48), cycloolefin polymer (1.52), polycarbonate (1.59),polymethylmethacrylate (1.49), polystyrene (1.59).

The mean refractive index and the film thickness are inputted in KOBRA21ADH or WR, nx, ny and nz are calculated therewith. From thethus-calculated data of nx, ny and nz, Nz=(nx−nz)/(nx−ny) is furthercalculated.

In the invention, “slow axis” of the retardation film and others meansthe direction in which the refractive index is the largest. “Visiblelight region” is from 380 nm to 780 nm. Unless otherwise specificallyindicated, the wavelength at which a refractive index is measured isλ=550 nm in a visible light region.

In this description, the numerical data, the numerical ranges and thequalitative expressions (for example, expressions of “equivalent”,“equal”) that are shown optical characteristics of respective memberssuch as a retardation film and a liquid crystal layer should beinterpreted to indicate the numerical data, the numerical ranges and theproperties including errors that are generally acceptable forliquid-crystal display devices and their constitutive members.

FIG. 1 is a schematic cross-sectional view of one example of aliquid-crystal display device of the invention. In this drawing,however, the relative relation in the thickness between the constitutivelayers does not always reflect the real relative relation therebetween.In the drawing, the top indicates the displaying plane side, and thebottom indicates the back side (backlight side).

The liquid-crystal display device shown in FIG. 1 comprises an IPS-modeliquid-crystal cell 10, and a pair of polarizing plates PLa and PLb onand below it. The polarizing plates PLa and PLb each comprise apolarizing element 12 a or 12 b, and a liquid-crystal cell-sideprotective film 14 a or 14 b and an outer protective film 16 a or 16 bfor protecting it. In this example, at least one of the protective films14 a, 14 b, 16 a and 16 b is a thermoplastic-resin film containing alactone ring-having polymer that satisfies a predetermined formula.Preferably, at least one of the liquid-crystal cell-side protectivefilms 14 a and 14 b is the thermoplastic-resin film; and more preferablyboth of them are the thermoplastic-resin film. The outer protectivefilms 16 a and 16 b may also be the thermoplastic-resin film, or may beany other polymer film such as a cellulose acylate film, a polycarbonatefilm, a norbornene-based film or the like.

In this example, the above-mentioned thermoplastic-resin film is used asat least one of the protective films 14 a, 14 b, 16 a and 16 b, therebyproducing the liquid-crystal display device free from a problem ofdisplay performance fluctuation depending on the ambient temperature andhumidity change.

The IPS-mode liquid-crystal cell 10 is not specifically limited, and maybe any one in which the electrode formed inside the cell may generate anelectric field having a component parallel to the substrate. For it, forexample, any ordinary IPS-mode liquid-crystal cell is usable. The angleof the electric field direction to the surface of the cell substrate ispreferably at most 20 degrees, more preferably at most 10 degrees, orthat is, it is desirable that the electric field is substantiallyparallel to the substrate surface. The electrode may be formedseparately on the upper and lower substrates, or may be formed only onone substrate. The electrode may have a structure of two layers combinedvia an insulating layer therebetween. Of the two-layered electrode, theelectrode of the lowermost layer may be a non-patterned electrode or alinear electrode. The upper electrode is preferably linear, but may haveany other form of a network, spiral or dotted form through which theelectric field from the lower layer electrode can pass; and a floatingelectrode having a neutral potential may be further added to thestructure. The insulating layer may be formed of an inorganic materialsuch as SiO or a nitride film, or an acrylic or epoxy-based organicmaterial.

The liquid-crystal material to be used in the liquid-crystal cell may bea nematic liquid crystal having a positive dielectric anisotropy Δ∈. Thethickness (gap) of the liquid-crystal layer may be controlled by polymerbeads. Glass beads, fibers as well as resinous columnar spacers may formthe same gap. In an IPS-mode liquid-crystal cell, in general, theproduct of the thickness d (μm) of the liquid-crystal layer and therefractive anisotropy Δn thereof, Δn·d may be from 0.2 to 1.2 μm or so;and for satisfying the requirement for device thickness reduction, thismay be from 0.2 to 0.5 μm or so in the invention.

Materials for use in producing various members usable in theliquid-crystal display device of the invention, and a method forproducing the device are described in detail hereinunder.

[Thermoplastic-Resin Film Containing Lactone Ring-Having Polymer]

In the invention, used is a polarizing plate comprising athermoplastic-resin film containing a lactone ring-having polymer, andthe film satisfies the following formulas (I) and (II). Thethermoplastic-resin film is preferably a protective film of a polarizingelement, and more preferably, it is a protective film thereof disposedon the side of the liquid-crystal cell.

0≦|Re(630)|≦10, and |Rth(630)|≦25  (I)

|Re(400)−Re(700)|≦10, and |Rth(400)−Rth(700)|≦35  (II)

By compensating birefringence of the IPS-mode liquid-crystal cell withretardation falling within the range satisfying the above formulas (I)and (II), the color shift to occur in the oblique direction in the blackstate may be thereby reduced. The present inventors have found that thethermoplastic-resin film containing the specific lactone ring-havingpolymer may satisfy the above-mentioned condition, and that, when thefilm is used as an optical compensation film for an IPS-modeliquid-crystal cell, then the optical performance fluctuation dependingon the ambient temperature/humidity change may be reduced, or that is,the optical compensation fluctuation may be thereby reduced. Abirefringent polymer film is generally so controlled that theconstitutive molecules may be aligned in one direction by stretching it;but naturally, the molecular axis direction in the stretched film mayfluctuate and the molecular axes therefore fluctuate in the film. Inparticular, when the absolute value of Re increases owing to theenvironmental temperature/humidity change, then the axial shift maybecome great, therefore causing retardation unevenness, and this is onereason for the front contrast reduction (e.g., light leakage in thenormal line direction to the displaying plane in the black state). Inthe invention, used is a thermoplastic-resin film that contains alactone ring-having polymer and has a small absolute value of Re.Accordingly, the absolute value of Re of the film in the invention maybe made nearer to almost 0 (zero) and the optical performancefluctuation depending on the ambient temperature/humidity environmentchange of the film may be reduced, and as a result, the molecular axisdirection fluctuation inevitable in a retardation polymer film isthereby prevented from surfacing. The thermoplastic-resin film,containing a lactone ring-having polymer, may have |Re(630)| of beingequal to or less than 5 nm and |Rth(630)| of being equal to or less than15 nm. For more ideal optical compensation in the IPS-modeliquid-crystal cell in the invention, preferably, |Re(400)−Re(700)| isequal to or less than 5 nm and |Rth(400)−Rth(700)| is equal to or lessthan 10 nm. The thermoplastic-resin film, containing a lactonering-having polymer, satisfies the optical characteristics.

Preferably, Re and Rth of the thermoplastic-resin film do not changedepending on the ambient temperature. Preferably, Re{T} and Rth{T} (Tmeans the temperature (° C.) at which the data is measured) of thethermoplastic-resin film at a wavelength of 550 nm satisfy the followingformulas (III) and (IV),

|Re{50}−Re{25}|<5  (III)

|Rth{50}−Rth{25}|<10  (IV)

and more preferably the following formulas (III)′ and (IV)′.

|Re{50}−Re{25}|<3  (III)′

|Rth{50}−Rth{25}|<5  (IV)′

In measuring Re{T} and Rth{T}, the film is left at the temperature T° C.for at least 1 hour, and then measured.

Preferably, Re and Rth of the thermoplastic-resin film do not changedepending on the ambient humidity. Preferably, Re[H] and Rth[H] (H meansthe relative humidity (%) at which the data is measured) of thethermoplastic-resin film at a wavelength of 550 nm satisfy the followingformulas (V) and (VI),

|Re[80]−Re[10]|<5  (V)

|Rth[80]−Rth[10]|<10  (VI)

and more preferably the following formulae (V)′ and (VI)′.

|Re[80]−Re[10]|<3  (V)′

|Rth[80]−Rth[10]|<5  (VI)′

In measuring Re[H] and Rth[H], the film is left at the humidity H for atleast 1 hour, and then measured.

The major ingredient of the thermoplastic-resin film is selected fromlactone ring-having polymers, and preferably, selected from polymershaving a lactone ring structure of the following formula (1):

In the formula, R¹, R² and R³ each independently represent a hydrogenatom, or an organic residue having from 1 to 20 carbon atoms. Theorganic residue may contain an oxygen atom.

The content of the lactone ring structure of formula (1) in the lactonering-having polymer structure is preferably from 5 to 90% by mass, morepreferably from 10 to 70% by mass, even more preferably from 10 to 60%by mass, still more preferably from 10 to 50% by mass. When the contentof the lactone ring structure of formula (1) in the lactone ring-havingpolymer structure is at least 5% by mass, then the film may havesufficient heat resistance, solvent resistance and surface hardness.When the content of the lactone ring structure of formula (1) in thelactone ring-having polymer structure is at most 90% by mass, then thepolymer may have better shapability and processability.

The lactone ring-having polymer may have any other structure than thelactone ring structure of formula (1). Not specifically defined,examples of the structure other than the lactone ring structure offormula (1) preferably include polymer structure units (repetitivestructure units) to be constructed by polymerization of at least oneselected from (meth)acrylates, hydroxyl group-containing monomers,unsaturated carboxylic acids and monomers of the following formula (2),as described hereinunder.

In the formula, R⁴ represents a hydrogen atom or a methyl group; Xrepresents a hydrogen atom, an alkyl group having from 1 to 20 carbonatoms, an aryl group, an acetate group (—OAc; Ac represents an acetyl)),a cyano group (—CN), a group —CO—R⁵ or a group —CO—O—R⁶; R⁵ and R⁶ eachrepresent a hydrogen atom or an organic residue having from 1 to 20carbon atoms.

The content of the other structure than the lactone ring structure offormula (1) in the lactone ring-having polymer structure is preferablyfrom 10 to 95% by mass, more preferably from 10 to 90% by mass, evenmore preferably from 40 to 90% by mass, still more preferably from 50 to90% by mass, when the other structure is a polymer structure unit(repetitive structure unit) constructed by polymerization of a(meth)acrylate; the content is preferably from 0 to 30% by mass, morepreferably from 0 to 20% by mass, even more preferably from 0 to 15% bymass, still more preferably from 0 to 10% by mass, when the otherstructure is a polymer structure unit (repetitive structure unit)constructed by polymerization of a hydroxyl group-containing monomer.When the other structure is a polymer structure unit (repetitivestructure unit) constructed by polymerization of an unsaturatedcarboxylic acid, its content is preferably from 0 to 30% by mass, morepreferably from 0 to 20% by mass, even more preferably from 0 to 15% bymass, still more preferably from 0 to 10% by mass. When the otherstructure is a polymer structure unit (repetitive structure unit)constructed by polymerization of a monomer of formula (2), its contentis preferably from 0 to 30% by mass, more preferably from 0 to 20% bymass, even more preferably from 0 to 15% by mass, still more preferablyfrom 0 to 10% by mass.

The production method for the lactone ring-having polymer is notspecifically limited. For example, the polymer may be prepared asfollows. A polymer (a) having a hydroxyl group and an ester group in themolecular chain is prepared by polymerization, and then subjected to athermal treatment to carryout a lactone ring-forming condensationreaction and to introduce a lactone ring structure into the polymer.

In the polymerization step, for example, a monomer compositioncontaining a monomer of the following formula (3) may be polymerized togive a polymer having a hydroxyl group and an ester group in themolecular chain.

In the formula, R⁵ and R⁶ each independently represent a hydrogen atomor an organic residue having from 1 to 20 carbon atoms.

Examples of the monomer of formula (3) include methyl2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, tert-butyl2-(hydroxymethyl)acrylate. Of those, preferred are methyl2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate in pointof their effect of improving heat resistance; and more preferred ismethyl 2-(hydroxymethyl)acrylate. One or more different types of themonomers of formula (1a) may be used either singly or as combined.

The content of the monomer of formula (3) in the monomer composition tobe polymerized in the polymerization step is preferably from 5 to 90% bymass, more preferably from 10 to 70% by mass, even more preferably from10 to 60% by mass, still more preferably from 10 to 50% by mass. Whenthe content of the monomer of formula (3) in the monomer composition tobe polymerized in the polymerization step is at least 5% by mass, thenthe film may have sufficient heat resistance, solvent resistance andsurface hardness. When content of the monomer of formula (3) in themonomer composition to be polymerized in the polymerization step is atmost 90% by mass, then gellation may be prevented in lactone cyclizationand a polymer having better shapability and processability may beobtained.

The monomer composition to be polymerized in the polymerization step maycontain any other monomer than the monomer of formula (3). Notspecifically defined, preferred examples of the other monomer include,for example, (meth)acrylates, hydroxyl group-containing monomers,unsaturated carboxylic acids, and monomers represented by formula (2).One or more such other monomers than the monomer of formula (1a) may beused herein either singly or as combined.

In the formula, R⁴ represents a hydrogen atom or a methyl group; Xrepresents a hydrogen atom, an alkyl group having from 1 to 20 carbonatoms, an aryl group, an acetate group (—OAc; Ac represents an acetyl)),a cyano group (—CN), a group —CO—R⁵ or a group —CO—O—R⁶; R⁵ and R⁶ eachrepresent a hydrogen atom or an organic residue having from 1 to 20carbon atoms.

Not specifically defined, the (meth)acrylates may be any (meth)acrylatesexcept the monomer of formula (3), and examples of the (meth)acrylateinclude acrylates such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, tert-butyl acrylate, cyclohexyl acrylate,and benzyl acrylate; methacrylates such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, andbenzyl methacrylate. One or more of these may be used either singly oras combined. Of those, especially preferred is methyl methacrylate asthe film may have excellent heat resistance and transparency.

In the embodiment where the other (meth)acrylate than the monomer offormula (3) is used, its content in the monomer composition to bepolymerized in the polymerization step is preferably from 10 to 95% bymass, more preferably from 10 to 90% by mass, even more preferably from40 to 90% by mass, still more preferably from 50 to 90% by mass, forsufficiently exhibiting the effect of the invention.

Not specifically defined, the hydroxyl group-containing monomers may beany hydroxyl group-containing monomers except the monomer of formula(3), and examples of the hydroxyl group-containing monomer includeα-hydroxymethylstyrene, α-hydroxyethylstyrene; (2-hydroxyalkyl)acrylatessuch as methyl 2-(hydroxyethyl)acrylate; and 2-(hydroxyalkyl)acrylicacids such as 2-(hydroxyethyl)acrylic acid. One or more of these may beused either singly or as combined.

Where the hydroxyl group-containing monomer except the monomer offormula (3) is used, its content in the monomer composition to bepolymerized in the polymerization step is preferably from 0 to 30% bymass, more preferably from 0 to 20% by mass, even more preferably from 0to 15% by mass, still more preferably from 0 to 10% by mass, forsufficiently exhibiting the effect of the invention.

Examples of the unsaturated carboxylic acid include acrylic acid,methacrylic acid, crotonic acid, α-substituted acrylic acids,α-substituted methacrylic acids. One or more of these may be used eithersingly or as combined. Of those, more preferred are acrylic acid andmethacrylic acid as capable of sufficiently exhibiting the effect of theinvention.

In the embodiment where unsaturated carboxylic acid is used, its contentin the monomer composition to be polymerized in the polymerization stepis preferably from 0 to 30% by mass, more preferably from 0 to 20% bymass, even more preferably from 0 to 15% by mass, still more preferablyfrom 0 to 10% by mass, for sufficiently exhibiting the effect of theinvention.

Examples of the monomer represented by formula (2) include styrene,vinyltoluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone,ethylene, propylene, vinyl acetate. One or more of these may be usedeither singly or as combined. Of those, more preferred are styrene andα-methylstyrene as capable of sufficiently exhibiting the effect of theinvention.

In the embodiment where the monomer of formula (2) is used, its contentin the monomer composition to be polymerized in the polymerization stepis preferably from 0 to 30% by mass, more preferably from 0 to 20% bymass, even more preferably from 0 to 15% by mass, still more preferablyfrom 0 to 10% by mass, for sufficiently exhibiting the effect of theinvention.

The polymerization temperature and the polymerization time varydepending on the type of the monomers used and the ratio thereof.Preferably, the polymerization temperature is from 0 to 150° C., and thepolymerization time is from 0.5 to 20 hours; more preferably, thepolymerization temperature is from 80 to 140° C., and the polymerizationtime is from 1 to 10 hours.

In the polymerization mode using a solvent, the polymerization solventis not specifically defined. Examples of the solvent include aromatichydrocarbon solvents such as toluene, xylene, ethylbenzene; ketonesolvents such as methyl ethyl ketone, methyl isobutyl ketone; ethersolvents such as tetrahydrofuran. One or more of these may be usedeither singly or as combined. When the boiling point of the solvent usedis too high, then the residual volatile fraction remaining in thefinally obtained lactone ring-having polymer may increase. Therefore,the boiling point of the solvent is preferably from 50 to 200° C.

In polymerization, a polymerization initiator may be added, if desired.Not specifically defined, examples of the polymerization initiatorinclude organic peroxides such as cumene hydroperoxide,diisopropylbenzene hydroperoxide, di-tert-butyl peroxide, lauroylperoxide, benzoyl peroxide, tert-butylperoxyisopropyl carbonate,tert-amylperoxy-2-ethyl hexanoate; and azo compounds such as2,2′-azobis(isobutyronitrile), 1,1′-azobis(cyclohexanecarbonitrile),2,2′-azobis(2,4-dimethylvaleronitrile). One or more of these may be usedeither singly or as combined. Not specifically defined, the amount ofthe polymerization initiator to be used may be suitably determineddepending on the combination of the monomers to be used and the reactioncondition.

In polymerization, it is desirable that the concentration of the polymerformed in the polymerization reaction mixture is controlled to be atmost 50% by mass, for preventing the reaction liquid from gelling.Concretely, in the embodiment where the concentration of the polymerformed in the polymerization reaction mixture is more than 50% by mass,it is desirable that a polymerization solvent is suitably added to thepolymerization reaction mixture so as to make the mixture have a polymerconcentration of at most 50% by mass. The concentration of the polymerformed in the polymerization reaction mixture is more preferably at mostby mass, even more preferably at most 40% by mass. However, when theconcentration of the polymer in the polymerization reaction mixture istoo low, then the producibility may lower. Therefore, the concentrationof the polymer in the polymerization reaction mixture is preferably atleast 10 by mass, more preferably at least 20% by mass.

The mode of suitably adding the polymerization solvent to thepolymerization reaction mixture is not specifically defined. Thepolymerization solvent may be continuously added, or may be addedintermittently. Thus controlling the concentration of the polymer formedin the polymerization reaction mixture may more sufficiently prevent thereaction liquid from gelling, and in particular, even in a case wherethe proportion of the hydroxyl group and the ester group in themolecular chain is increased so as to increase the lactone ring contentratio to thereby enhance the heat resistance of the polymer, thegellation may be sufficiently prevented. The polymerization solvent tobe added may be the same type as that of the solvent used in the initialstage of monomer feeding for polymerization, or may differ from thelatter. Preferably, however, the polymerization solvent to be added isthe same type as that of the solvent used in the initial stage ofmonomer feeding for polymerization. A single solvent or a mixed solventof two or more different types of solvents may be used as thepolymerization solvent to be added.

The polymerization reaction mixture obtained at the time at which thepolymerization step as above has ended generally contains a solvent inaddition to the formed polymer; however, it is unnecessary to completelyremove the solvent to take out the polymer as a solid state, and it isdesirable to introduce the polymer still containing the solvent to thesubsequent lactone ring-forming condensation step. If desired, however,the polymer is once taken out as a solid state, and a suitable solventmay be newly added to the subsequent lactone ring-forming condensationstep.

The polymer obtained in the polymerization step is a polymer (a) havinga hydroxyl group and an ester group in the molecular chain, and theweight-average molecular weight of the polymer (a) is preferably from1,000 to 2,000,000, more preferably from 5,000 to 1,000,000, even morepreferably from 10,000 to 500,000, still more preferably from 50,000 to500,000. The polymer (a) obtained in the polymerization step is heatedin the subsequent lactone ring-forming condensation step, in which alactone ring structure is introduced into the polymer to give a lactonering-having polymer.

The reaction of introducing a lactone ring structure into the polymer(a) comprises heating the polymer (a) for cyclization and condensationof the hydroxyl group and the ester group existing in the molecularchain of the polymer (a) to give a lactone ring structure, in which thecyclization and condensation gives an alcohol as a side product. Thelactone ring structure formed in the molecular chain of the polymer (themain skeleton of the polymer) gives high heat resistance to theresulting polymer. When the reactivity of the cyclization condensationreaction to give the lactone ring structure is poor, then it isundesirable since the heat resistance could not be sufficiently enhancedor the polymer may be condensed during its shaping by the heat treatmentin shaping it and the formed alcohol may remain in the shaped article asbubbles or silver streaks.

The lactone ring-having polymer thus obtained in the lactonering-forming condensation step preferably has the lactone ring structureof the above-mentioned formula (1).

The method of carrying out the thermal treatment of the polymer (a) isnot specifically, for which, any known method is usable. For example,the solvent-containing polymerization reaction mixture obtained in thepolymerization step may be directly heated as it is. In the presence ofa solvent, it may be heated with a ring-closing catalyst. A heatingfurnace of a reaction device equipped with a vacuum unit or a degassingunit for removing a volatile ingredient, or an extruder equipped with adegassing unit may be used for the thermal treatment.

In the cyclization condensation reaction, other thermoplastic resins maybe coexisted with the polymer (a). Also in the cyclization condensationreaction, if desired, an ordinary esterification catalyst ortransesterification catalyst such as p-toluenesulfonic acid may be usedas a cyclization condensation catalyst; or an organic carboxylic acidsuch as acetic acid, propionic acid, benzoic acid, acrylic acid ormethacrylic acid may be used as a catalyst. As described in JPA Nos. syo61-254608 and syo 61-261303, a basic compound, an organic carboxylicacid salt and a carbonic acid salt may also be used.

One or more organic phosphor compounds may be used for the cyclizationcondensation reaction. Examples of the usable organic phosphor compoundinclude alkyl or aryl phosphorous acids, which may change to tautomersthereof, alkyl or aryl phosphinous acids, and mono- or di-esters thereofsuch as methyl phosphorous acid, ethyl phosphorous acid and phenylphosphorous acid; dialkyl or diaryl phosphine acids and esters thereofsuch as dimethyl phosphine acid, diethyl phosphine acid, diphenylphosphine acid, phenyl methyl phosphine acid, phenyl ethyl phosphineacid; alkyl or aryl phosphonic acids and mono- or di-esters thereof suchas methyl phosphonic acid, ethyl phosphonic acid, trifluoro methylphosphonic acid and phenyl phosphonic acid; alkyl or aryl phosphinousacids and esters thereof such as methyl phosphinous acid, ethylphosphinous acid, and phenyl phosphinous acid; phosphite mono-, di- ortri-esters such as methyl phosphite, ethyl phosphite, phenyl phosphite,dimethyl phosphite, diethyl phosphite, diphenyl phosphite, trimethylphosphite, triethyl phosphite and triphenyl phosphite; phosphoric mono-,di- or tri-esters such as methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate,stearyl phosphate, isostearyl phosphate, phenyl phosphate, dimethylphosphate, diethyl phosphate, di-2-ethylhexyl phosphate, di-isodecylphosphate, di-lauryl phosphate, di-steraryl phosphate, di-isostearylphosphate, di-phenyl phosphate, trimethyl phosphate, triethyl phosphate,tri-isodecyl phosphate, tri-lauryl phosphate, tri-stearyl phosphate,tri-isostearyl phosphate and tri-phenyl phosphate; mono-, di- ortri-alkyl or aryl phosphines such as methyl phosphine, ethyl phosphine,phenyl phosphine, phenyl phosphine, dimethyl phosphine, diethylphosphine, diphenyl phosphine, trimethyl phosphine, triethyl phosphineand triphenyl phosphine; alkyl or aryl halide phosphine such as methyldichloro phosphine, ethyl dichloro phosphine, phenyl dichloro phosphine,dimethyl chloro phosphine, diethyl chloro phosphine and diphenyl chlorophosphine; mono-, di- or tri-alkyl or aryl oxide phosphines such asmethyl oxide phosphine, ethyl oxide phosphine, phenyl oxide phosphine,dimethyl oxide phosphine, diethyl oxide phosphine, diphenyl oxidephosphine, trimethyl oxide phosphine, triethyl oxide phosphine, andtriphenyl oxide phosphine; and tetra alkyl or aryl phosphonium chloridessuch as tetra-methyl phosphorous chloride, tetra-ethyl phosphorouschloride and tetra-phenyl phosphorous chloride. One or more type oforganic phosphorous compounds may be sued. Among these compounds, interms of high catalyst-activity and low-coloration, preferred are alkylor aryl phosphorous acids, phosphite mono- or di-esters, phosphoricmono- or di-esters, and alkyl or aryl phosphonic acids; more preferredare alkyl or aryl phosphorous acids, phosphite mono- or di-esters, andphosphoric mono- or di-esters; and even more preferred are alkyl or arylphosphorous acids and phosphite mono- or di-esters.

The amount of the catalyst to be added is not also specifically defined.Preferably, it may be from 0.001 to 5% by mass of the polymer (a), morepreferably from 0.01 to 2.5% by mass, even more preferably from 0.01 to1% by mass, still more preferably from 0.05 to 0.5% by mass. When theamount of the catalyst is less than 0.001% by mass, the ratio of thecyclization condensation reaction may be accelerated sufficiently. Onthe other hand, when the amount of the catalyst is more than 5% by mass,the obtained polymer may be colored or cross-linked, and the crosslinkedpolymer may be not suitable for melt-film processing.

The catalyst may be added in the initial stage of reaction, or duringthe reaction, or both in the two.

Preferably, the cyclization condensation reaction is carried out in thepresence of a solvent, and the cyclization condensation is combined witha degassing step. The cyclization condensation may be combined with adegassing step all the time during the reaction, and the cyclizationcondensation may not be combined with a degassing step all the timeduring the reaction but may be combined with it in a part of thereaction. In these embodiments, the alcohol formed as a side productduring the cyclization condensation may be forcedly degassed, andtherefore, the reaction equilibrium is advantageous for the productside.

The degassing step comprises removing the volatile fractions such assolvent and unreacted monomer, and the alcohol formed as a side productby the cyclization condensation for lactone ring structure formation,optionally under reduced pressure and under heat. When the removal isinsufficient, then the amount of the remaining volatile fractions in theformed resin may increase, therefore causing various problems in thatthe shaped product of the resin may be colored owing to thediscoloration of the volatile fractions during shaping or the shapedproduct may have shaping failures such as bubbles and silver streaks.

In the embodiment where the cyclization condensation is combined with adegassing step all the time during the reaction, the apparatus to beused is not specifically defined. Preferably used in the embodiment is adegassing unit comprising a heat exchanger and a degassing tank, or avented extruder, or a combination of the degassing unit and the ventedextruder connected in series. More preferred is a degassing unitcomprising a heat exchanger and a degassing tank, or a vented extruder.

The reaction temperature in the embodiment where the above-mentioneddegassing unit comprising a heat exchanger and a degassing tank is usedis preferably within a range of from 150 to 350° C., more preferablyfrom 200 to 300° C. When the reaction temperature is not lower than 150°C., then the cyclization condensation may go on sufficiently and theremaining volatile fractions may be reduced; and when it is not higherthan 350° C., then the polymer may be prevented from being colored ordecomposed.

The reaction pressure in the embodiment where the above-mentioneddegassing unit comprising a heat exchanger and a degassing tank is usedis preferably within a range of from 931 to 1.33 hPa (700 to 1 mmHg),more preferably from 798 to 66.5 hPa (600 to 50 mmHg). When the pressureis at most 931 hPa, then the volatile fractions including alcohol may besufficiently prevented from remaining in the system; and when it is atleast 1.33 hPa, the industrial performance of the method may be better.

When the above-mentioned vented extruder is used, the number of thevents may be one or more. Preferably, the extruder has plural vents.

In the embodiment where the vented extruder is used, the reactiontemperature is preferably within a range of from 150 to 350° C., morepreferably from 200 to 300° C. When the temperature is not lower than150° C., the cyclization condensation may go on sufficiently and theremaining volatile fractions may be reduced; and when it is not higherthan 350° C., then the polymer may be prevented from being colored ordecomposed.

The reaction pressure in the embodiment where the above-mentioned ventedextruder is used is preferably within a range of from 931 to 1.33 hPa(700 to 1 mmHg), more preferably from 798 to 13.3 hPa (600 to 10 mmHg).When the pressure is at most 931 hPa, then the volatile fractionsincluding alcohol may be sufficiently prevented from remaining in thesystem; and when it is at least 1.33 hPa, the industrial performance ofthe method may be better.

In the embodiment where the cyclization condensation is combined with adegassing step all the time during the reaction, the physical propertiesof the obtained lactone ring-having polymer may worsen under a severeheat treatment condition as described hereinunder; and therefore in theembodiment, it is desirable that the above-mentioned alcohol removalcatalyst is used and the reaction is attained by the use of a ventedextruder under a condition as mild as possible.

In the embodiment where the cyclization condensation is combined with adegassing step all the time during the reaction, it is desirable thatthe polymer (a) formed in the polymerization step is introduced into thecyclization condensation reactor system along with a solvent thereinto,but in this embodiment, if desired, the polymer may be once again led topass through the above-mentioned reactor device such as a ventedextruder.

In another embodiment, the cyclization condensation may be not combinedwith a degassing step all the time during the reaction but is combinedwith it in a part of the reaction. For example, the device in which thepolymer (a) has been produced is further heated, and if desired, this iscombined with a degassing step in which the cyclization condensation ofthe polymer is partly attained in some degree, and then the polymer isprocessed in the subsequent cyclization condensation step combined witha degassing step, in which the reaction of the polymer is thuscompleted.

In the above-mentioned embodiment where the cyclization condensation iscombined with a degassing step all the time during the reaction, forexample, the polymer (a) may be partly decomposed before the cyclizationcondensation owing to the difference in the heat history thereof in thehigh-temperature heat treatment at around 250° C. or higher in adouble-screw extruder, and the physical properties of the obtainedlactone ring-having polymer may be thereby worsened. To solve theproblem, prior to the cyclization condensation combined with thedegassing step, the polymer is previously processed for cyclizationcondensation in some degree; and in that manner, the reaction conditionin the latter step of subsequent cyclization condensation of the polymermay be relaxed in some degree and the physical properties of theobtained lactone ring-having polymer may be prevented from beingworsened. Accordingly, this embodiment is preferred. More preferably,the degassing step is started after a period of time from the start ofthe cyclization condensation, or that is, the polymer (a) produced inthe polymerization step is processed for cyclization condensation of thehydroxyl group and the ester group existing in the molecular chainthereof so that the cyclization condensation degree of the polymer isincreased in some degree, and then the polymer is again processed forcyclization condensation as combined with a degassing step. Concretely,for example, the polymer is processed in a pot-type reactor in thepresence of a solvent therein for cyclization condensation in somedegree, and then, this is transferred into a reactor equipped with adegassing unit, for example, into a degassing system comprising a heatexchanger and a degassing tank, or a vented extruder, in which thecyclization condensation of the polymer is completed. This is an exampleof the preferred embodiment. Especially in this embodiment, it is moredesirable that a catalyst for cyclization condensation exists in thereaction system.

As described in the above, the method of cyclization condensationsimultaneously combined with a degassing step, in which the hydroxylgroup and the ester group existing in the molecular chain of the polymer(a) obtained in the polymerization step are previously processed forcyclization condensation to increase the cyclization condensation degreeof the polymer in some degree, is a preferred embodiment for obtainingthe lactone ring-having polymer for use in the invention. According tothis embodiment, a lactone ring-having polymer having a higher glasstransition temperature, having a higher degree of cyclizationcondensation and having more excellent heat resistance can be obtained.In this embodiment, regarding the intended degree of cyclizationcondensation, it is desirable that the mass reduction ratio in the rangefalling between 150° C. and 300° C. in the dynamic TG determinationshown in Examples given hereinunder is at most 2%, more preferably atmost 1.5%, even more preferably at most 1%.

The reactor employable for the previous cyclization condensation to beattained prior to the cyclization condensation simultaneously combinedwith a degassing step is not specifically defined. Preferably, thereactor is an autoclave, a pot-type reactor, or a degassing unitcomprising a heat exchanger and a degassing tank. In addition, a ventedextruder favorable for the cyclization condensation simultaneouslycombined with a degassing step is also favorably used. More preferred isan autoclave or a pot-type reactor. However, even when any other reactorsuch as a vented extruder is used, the cyclization condensation may beattained under the same reaction condition as that in an autoclave or apot-type reactor, by controlling the venting condition to a moremoderate one, or by not venting the extruder, or by controlling thetemperature condition, the barrel condition, the screw form and thescrew driving condition.

For the previous cyclization condensation to be attained prior to thecyclization condensation simultaneously combined with a degassing step,preferably employed is (i) a method of adding a catalyst to a mixturethat contains the polymer (a) formed in the polymerization step and asolvent, and heating it, or (ii) a method of heating the mixture in theabsence of a catalyst. The method (i) and (ii) may be attained underpressure.

The “mixture containing the polymer (a) and a solvent” to be introducedinto the cyclization condensation system in the lactone ring-formingstep may be the polymerization reaction mixture obtained in thepolymerization step as it is; or the solvent may be once removed fromthe mixture, and a different solvent suitable for cyclizationcondensation may be newly added to it.

The solvent that may be added to the previous cyclization condensationto be attained prior to the cyclization condensation simultaneouslycombined with a degassing step is not specifically defined. For example,the solvent includes aromatic hydrocarbons such as toluene, xylene,ethylbenzene; ketones such as methyl ethyl ketone, methyl isobutylketone; and chloroform, DMSO, tetrahydrofuran. Preferably, the solventis the same as that usable in the polymerization step.

The catalyst to be added in the above step (i) may be ordinaryesterification or interesterification catalysts such asp-toluenesulfonic acid, as well as basic compounds, organic carboxylicacid salts, carbonic acid salts. Preferred are the above-mentionedorganic phosphorus compounds. The time when the catalyst is added is notspecifically defined. The catalyst may be added in the initial stage ofreaction, or during the reaction, or both in the two. The amount of thecatalyst to be added is not also specifically defined. Preferably, itmay be from 0.001 to 5% by mass of the polymer (a), more preferably from0.01 to 2.5% by mass, even more preferably from 0.01 to 1% by mass,still more preferably from 0.05 to 0.5% by mass. The heating temperatureand the heating time in the step (i) are not specifically defined. Theheating temperature is preferably not lower than room temperature, morepreferably not lower than 50° C.; and the heating time is preferablyfrom 1 to 20 hours, more preferably from 2 to 10 hours. When the heatingtemperature is low, or when the heating time is short, then it isunfavorable since the conversion in cyclization condensation may lower.However, when the heating time is too long, then it is also unfavorablesince the resin may color or decompose.

For the above method (ii), for example, employable is a method ofheating the polymerization mixture obtained in the polymerization step,directly as it is, using a pressure-resistant pot reactor. The heatingtemperature is preferably not lower than 100° C., more preferably notlower than 150° C. The heating time is preferably from 1 to 20 hours,more preferably from 2 to 10 hours. When the heating temperature is low,or when the heating time is short, then it is unfavorable since theconversion in cyclization condensation may lower. However, when theheating time is too long, then it is also unfavorable since the resinmay color or decompose.

The above methods (i) and (ii) may be attained under pressure with noproblem, depending on the condition thereof.

During the previous cyclization condensation to be attained prior to thecyclization condensation simultaneously combined with a degassing step,a part of the solvent may spontaneously vaporize during the reactionwith no problem.

At the end of the previous cyclization condensation to be attained priorto the cyclization condensation simultaneously combined with a degassingstep, or that is, just before the start of the degassing step, the massreduction ratio in the range falling between 150° C. and 300° C. indynamic TG determination is preferably at most 2%, more preferably atmost 1.5%, even more preferably at most 1%. When the mass reductionratio is at most 2%, then the cyclization condensation reactivity may beincreased up to a sufficiently high level during the successivecyclization condensation simultaneously combined with a degassing step,and the obtained lactone ring-having polymer may therefore have betterphysical properties. During the cyclization condensation, any otherthermoplastic resin may be added to the system in addition to thepolymer (a).

In the embodiment where the hydroxyl group and the ester group existingin the molecular chain of the polymer (a) obtained in the polymerizationstep are previously cyclized and condensed so as to increase theconversion in cyclization condensation reaction in some degree and wherethe previous cyclization condensation is followed by the successivecyclization condensation simultaneously combined with a degassing step,the polymer obtained in the previous cyclization condensation step (inthe polymer, the hydroxyl group and the ester group existing in themolecular chain are at least partly cyclized and condensed) and asolvent may be introduced into the subsequent process of cyclizationcondensation simultaneously combined with a degassing step directly assuch; or if desired, the polymer (in the polymer, the hydroxyl group andthe ester group existing in the molecular chain are at least partlycyclized and condensed) may be isolated and a solvent may be newly addedthereto or the polymer may be processed for any other treatment, andthereafter it may be introduced into the subsequent cyclizationcondensation step simultaneously combined with a degassing step.

The degassing step is not always completed simultaneously with thecyclization condensation, but it may be completed after a while from theend of the cyclization condensation.

The lactone ring-having polymer has a weight-average molecular weight ofpreferably from 1,000 to 2,000,000, more preferably from 5,000 to1,000,000, even more preferably from 10,000 to 500,000, still morepreferably from 50,000 to 500,000.

Preferably, the mass reduction ratio of the lactone ring-having polymer,as measured within a range of from 150 to 300° C. through dynamic TGanalysis, is at most 1 more preferably at most 0.5%, even morepreferably at most 0.3%.

As having a high conversion in cyclization condensation, the lactonering-having polymer is free from the drawbacks of bubbles or silverstreaks to be in the shaped articles thereof. Further, owing to the highconversion in cyclization condensation thereof, the lactone ringstructure may be sufficiently introduced into the polymer, andtherefore, the obtained lactone ring-having polymer may havesufficiently high heat resistance.

Preferably, the degree of coloration (YI) of the lactone ring-havingpolymer, as measured in a 15% mass chloroform solution, is at most 6,more preferably at most 3, even more preferably at most 2, mostpreferably at most 1. When the degree of coloration (YI) is not higherthan 6, then the polymer may be prevented from coloring and may havehigh transparency.

Preferably, the temperature for 5% mass reduction in thermal massanalysis (TG) of the lactone ring-having polymer is not lower than 330°C., more preferably not lower than 350° C., even more preferably notlower than 360° C. The temperature for 5% mass reduction in thermal massanalysis (TG) is an index of thermal stability. When the temperature isnot lower than 330° C., then the polymer may exhibit sufficient thermalstability.

Preferably, the lactone ring-having polymer has a glass transitiontemperature (Tg) of not lower than 115° C., more preferably not lowerthan 125° C., even more preferably not lower than 130° C., still morepreferably not lower than 135° C., most preferably not lower than 140°C.

Preferably, the total amount of the volatile residues in the lactonering-having polymer is at most 1,500 ppm, more preferably at most 1,000ppm. When the total amount of the volatile residues is at most 1,500ppm, then the polymer may be effectively prevented from having shapingfailures of coloration, bubbles or silver streaks to be caused by thedeterioration of the polymer in shaping it.

Preferably, the whole light transmittance of the injection-moldedarticle of the lactone ring-having polymer, as measured according to themethod of ASTM-D-1003, is at least 85%, more preferably at least 88%,even more preferably at least 90%. The whole light transmittance is anindex of transparency.

The thermoplastic-resin film to be used in the invention comprises thelactone ring-having polymer as a major ingredient, and, morespecifically, the amount of lactone ring-having polymer in the film ispreferably from 50 to 100% by mass, more preferably from 60 to 100% bymass, even more preferably from 70 to 100% by mass, and even much morepreferably from 80 to 100% by mass. When the amount of the lactonering-having polymer is less than 50% by mass, the effect of theinvention may be insufficient.

The thermoplastic-resin film may further comprise one or more polymersother than the lactone ring-having polymer, examples of such otherpolymer(s) include olefin-polymers such as polyethylenes,polypropylenes, ethylene-propylene copolymers andpoly(4-methyl-1-pentene); vinyl halide-type polymers such as poly vinylchloride, poly vinylidene chloride and polyvinyl chloride resin;acryl-type polymers such as polymethyl methacrylates; polystyrenes,styrene-methyl methacrylate copolymers, styrene-acrylonitrilecopolymers, acrylonitrile-butadiene-styrene block copolymers; polyesterssuch as polyethylene terephthalates, polybutylene terephthalates andpolyethylene naphthalates; polyamides such as nylon 6, nylon 66 andnylon 610; polyacetals; polycarbonates; polyphenylene oxides;polyphenylene sulfides, polyether ketones; polysulfones;polyethersulfones; polyoxy benzyls; polyamide imides; and gum polymerssuch as ABS and ASA resins containing polybutadiene-type rubber oracryl-type rubber.

The amount of the other polymer(s) in the thermoplastic-resin film ispreferably from 0 to 50% by mass, more preferably from 0 to 40 by mass,even more preferably from 0 to 30% by mass and even much more preferablyfrom 0 to 20% by mass.

Various additives may be added to the thermoplastic-resin film. Theadditives include, for example, hindered phenol-based,phosphorus-containing or sulfur-containing antioxidants; stabilizerssuch as light-resistant stabilizers, weather-resistant stabilizers andthermal stabilizers; reinforcing materials such as glass fibers andcarbon fibers; LTV absorbents such as phenyl salicylate,(2,2′-hydroxy-5-methylphenyl)benzotriazole and 2-hydroxybenzophenone;near-IR absorbents; flame retardants such astris(dibromopropyl)phosphate, triallyl phosphate and antimony oxide;antistatic agents such as anionic, cationic or nonionic surfactants;colorants such as inorganic pigments, organic pigments and dyes; organicfillers and inorganic fillers; resin modifiers, plasticizers;lubricants, etc.

The content of the additives in the thermoplastic-resin film ispreferably from 0 to 5% by mass, more preferably from 0 to 2% by mass,even more preferably from 0 to 0.5% by mass.

The method for producing the thermoplastic-resin film is notspecifically defined. For example, a lactone ring-having polymer andother polymer and additive may be fully mixed in an ordinary knownmethod to prepare a thermoplastic-resin composition, and this may beformed into a film. Alternatively, a lactone ring-having polymer andother polymer and additive may be separately prepared in differentcontainers, and they may be mixed to give a uniform mixture, which maybe then formed into a film.

First, for producing a thermoplastic-resin composition, for example, theabove-mentioned film materials are pre-blended with an ordinary knownmixer such as an omni-mixer, and the resulting mixture is kneaded byextrusion. In this case, the mixer to be used for extrusion kneading isnot specifically defined, and usable are ordinary known mixers, forexample, extruders such as a single-screw extruder and a twin-screwextruder, as well as pressure kneaders.

For film formation, for example, employable are conventional known filmformation methods such as a solution-casting method, a melt extrusionmethod, a calendering method, a compression forming method, etc. Ofthose film formation methods, preferred is a solution-casting method anda melt extrusion method.

Examples of the solvent to be used in the solution casting methodinclude aromatic solvents such as benzene, toluene and xylene; aliphatichydrocarbons such as cyclohexane and decalin; esters such as ethylacetate and butyl acetate; ketones such as acetone, methyl ethyl ketoneand methyl isobutyl ketone; alcohols such as methanol, ethanol,isopropanol, butanol, isobutanol, methyl cellosolve, ethyl cellosolveand butyl cellosolve; ethers such as tetrahydro furan and dioxane;halogenated hydrocarbons such as dichloro methane, chloroform and carbontetrachloride; dimethylformamide; and dimethylsulfoxide. One or moreselected from these solvents may be used either singly or as combined.

Examples of the apparatus for the solution casting method include a drumcasting machine, a band casting machine, and a spin coater.

The melt extrusion method may be carried out according to a T-die methodor an inflation method, in which the film-forming temperature ispreferably from 150 to 350° C., more preferably from 200 to 300° C.

According to the melt extrusion method employing a T-die, a T-die isattached to a known single screw extruder or twin screw extruder at theterminal portion thereof, and a film extruded is rolled up, and then arolled-up film is obtained. The temperature of the wind-up roll may becontrolled to stretch the film along the extrusion direction, or inother words, to stretch the film monoaxially. The film may be stretchedalong the direction orthogonal to the extrusion direction, or in otherwords the film may be subjected to a successive biaxial stretching orsimultaneous biaxial stretching treatment.

The thermoplastic-resin film may be a stretched or non-stretched film;and the thermoplastic-resin film may be a successivelybiaxially-stretched or simultaneous biaxially-stretched film. Bycarrying out a biaxially-stretching treatment, the mechanical strengthof the film may be improved, and the film properties may be improved. Byadding other thermoplastic resin(s) to the thermoplastic-resin filmcontaining a lactone-ring-having polymer as a major ingredient, it maybe possible to prevent the enhancement of retardation of film to besubjected to a stretching treatment and to obtain an optically isotropicfilm even if it is subjected to a stretching treatment.

Preferably, the stretching is effected at around the glass transitiontemperature of the polymer used as the film material. Concretely, thestretching temperature is preferably from (glass transitiontemperature−30° C.) to (glass transition temperature+100° C.), morepreferably from (glass transition temperature−20° C.) to (glasstransition temperature+80° C.). When the stretching temperature is notlower than the (glass transition temperature−30° C.), then the film maybe stretched at a sufficient draw ratio; and when the stretchingtemperature is not higher than the (glass transition temperature+100°C.), then the resin may well flow enough for stable stretching.

The draw ratio in stretching by area is preferably from 1.1 to 25 times,more preferably from 1.3 to 10 times. When the draw ratio is at least1.1 times, then the toughness of the stretched film may be increased;and on the contrary, when the draw ratio is at most 25 times, then theeffect of stretching may increase in accordance with the increased drawratio.

The stretching rate (in one direction) is preferably from 10 to20,000%/min, more preferably from 100 to 10,000%/min. When thestretching rate is at least 10%/min, then the time for obtaining thesufficient draw ratio may be shortened and the production cost may bethereby reduced. On the contrary, when the stretching rate is at most20,000%/min, then the film being stretched is prevented from being cut.

For stabilizing the optical isotropy and the mechanical propertiesthereof, the stretched film may be subjected to a thermal treatment suchas an anneal treatment. The thermal treatment may be carried out underthe general condition which has been used in the thermal treatments forthe conventional stretched films.

The thickness of the polymer film for use as the support in the secondinvention is preferably from 5 μm to 200 μm, more preferably from 10 μmto 100 μm. When the thickness is less than 5 μm, then the strength ofthe film may become worse and the film may curl up remarkably when beingsubjected to a durability test; but when the thickness is more than 200μm, then the transparency of the film may become worse and the moisturepermeability of the film may become so low that the drying ratio ofwater contained in the water-type adhesion.

The thermoplastic-resin film preferably has a surface wet tension of atleast 40 mN/m, more preferably at least 50 mN/m, even more preferably atleast 55 mN/m. When the surface wet tension is at least 40 mN/m, thenthe adhesion strength between the thermoplastic-resin film and any otherlayer, for example, a polarizing element or the like may be furtherenhanced. For controlling the surface wet tension thereof, for example,the film may be processed for conventional known surface treatment suchas corona discharge treatment, plasma treatment, ozone blasting, UVradiation, flame treatment or chemical treatment.

The thermoplastic-resin film may contain various additives. For example,a retardation controlling agent for reducing retardation in plane and/orretardation along the thickness direction of the film may be added tothe film. Adding such a retardation controlling agent to the film andoptionally stretching the film may make the film have desired opticalcharacteristics.

(Adhesive Layer)

In the invention, preferably, an adhesive layer is formed on the surfaceof the thermoplastic-resin film for enhancing the adhesiveness of thethermoplastic-resin film to a polarizing element. Preferably, theadhesive layer is formed of a polyurethane resin composition (includinga composition that contains a polyurethane resin and/or a precursorcapable of giving a polyurethane after reaction) and/or a compositioncontaining an amino group-having polymer (hereinafter these may bereferred to as “adhesive layer-coating composition”). The composition isprepared as a coating liquid, and this is applied onto at least onesurface of the thermoplastic-resin film and dried/cured or dried to formthe intended adhesive layer.

The thickness of the adhesive layer is preferably from 0.01 to 10 μm orso, more preferably from 0.05 to 3 μm or so, even more preferably from0.1 to 1 μm or so. When the thickness of the adhesive layer falls withinthe range, it is favorable since the adhesiveness thereof may besufficient and, in addition, in a water resistance or moistureresistance test, the polarizer may be hardly decolored or discolored.

The composition containing a polyurethane resin or containing aprecursor capable of giving a polyurethane resin after reaction, and theamino group-having polymer for use in forming the adhesive layer, andthe method for forming the adhesive layer are described in JPA No.2007-127893, paragraphs [0124] to [0175], and the description may bereferred to for the material of the adhesive layer and the method forforming the layer in the invention.

For controlling the surface wet tension, the surface of thethermoplastic-resin film or the surface of the adhesive layer to beformed optionally may be processed for conventional known surfacetreatment such as corona discharge treatment, plasma treatment, ozoneblasting, UV radiation, flame treatment or chemical treatment.

(Polarizing Element)

The polarizing element of the polarizing plate for use in the inventionmay be any of an iodine-containing polarizing film, a dichroicdye-containing polarizing film or a polyene-based polarizing film. Theiodine-based polarizing film and the dye-containing polarizing film maybe produced generally by the use of a polyvinyl alcohol film.

(Second Protective Film)

Preferably, the polarizing plate for use in the invention has a secondprotective film in addition to the thermoplastic-resin film. The secondprotective film is stuck to the surface of a polarizing element oppositeto the surface thereof to which the thermoplastic-resin film is notstuck. The second protective film may be formed of the same film as thatof the thermoplastic-resin film or may be any other polymer film, or acellulose acylate film, a polycarbonate film, a norbornene-based film orthe like.

(Adhesive)

In fabricating the polarizing plate for use in the invention, anadhesive may be used in sticking the thermoplastic-resin film or thesecond protective film to the polarizing element. More preferably, theabove-mentioned adhesive layer is formed on the surface of thethermoplastic-resin film, then the adhesive layer is stuck to the otherlayer with an adhesive. Examples of the usable adhesive include a PVAadhesive, a polyurethane adhesive, an acrylic adhesive and an isocyanateadhesive. One or more of these adhesives may be used herein eithersingly or as combined. Of those adhesives, especially preferred are apolyurethane adhesive and an isocyanate adhesive. The morphology of theadhesive is not specifically defined. For example, various types ofadhesives such as solvent-based adhesives, water-based adhesives andnon-solvent adhesives may be used.

Polyurethane adhesives, isocyanate adhesives, and reaction catalysts andadditives to be used for them as well as their amount are described indetail in JPA No. 2007-12789, paragraphs [0174] to [0194], and thedescription may be referred to for the adhesives usable in theinvention.

(Other Functional Layers)

The polarizing plate for use in the invention may have variousfunctional layers, for example, a non-glare layer, acontamination-preventing layer such as a photocatalyst layer, a hardcoat layer, an antireflection layer, a UV-blocking layer, a heatray-blocking layer, an electromagnetic wave-blocking layer, agas-barrier layer, etc. The materials and others for use in forming themare described in detail in JPA No. 2006-96960, paragraphs [0060] to[0065], and the description may be referred to for the materials forforming various functional layers in the invention.

(Another Polarizing Plate)

The polarizing plate usable along with the polarizing plate having thethermoplastic-resin film is not specifically defined. A polarizing platesimilarly having the thermoplastic-resin film may be used, or apolarizing plate having a protective film only of any other polymerfilm, for example, a cellulose acylate film, a polycarbonate film or anorbornene-based film may be used. Preferably used are two polarizingplates both having the thermoplastic-resin film, as enhancing the effectof the invention. In the embodiments where one polarizing plate alonehaving the thermoplastic-resin film is used, it is preferably disposedas the polarizing plate on the back side (PLb in FIG. 1).

The liquid-crystal display device of the invention is not limited to theconstitution shown in FIG. 1, and may have any other member. Forexample, a color filter may be disposed between the liquid-crystal celland the polarizing film. As will be described hereinunder, any otheroptical compensatory film may be disposed between the liquid-crystalcell and the polarizing plate. In the embodiments where the device is atransmission-type device, a cold cathode or hot cathode fluorescenttube, or a light source with a light-emitting diode, a filed emissionelement or an electroluminescent element may be disposed on the back.The liquid-crystal display device of the invention may be areflection-type device. In such a case, only one polarizing plate of theinvention may be disposed on the viewers' side, and a reflection film isdisposed on the back side of the liquid-crystal cell or on the innersurface of the lower substrate of the liquid-crystal cell.Needless-to-say, a front light with the above-mentioned light source maybe disposed on the viewers' side of the liquid-crystal cell.

The liquid-crystal display device of the invention includes aforward-looking type device, an image projection type device and aphotomodulation type device. The invention is especially effectivelyapplied to active matrix liquid-crystal display devices comprising a3-terminal or 2-terminal semiconductor element such as TFT or MIM.Needless-to-say, the invention is also effectively applicable to passivematrix liquid-crystal display devices such as typically STN-type devicesreferred to as time-sharing driving devices.

EXAMPLES

The invention is described more concretely with reference to thefollowing Examples, in which the material and the reagent used, theiramount and the ratio, the details of the treatment and the treatmentprocess may be suitably modified or changed not overstepping the spiritand the scope of the invention. Accordingly, the invention should not belimited by the Examples mentioned below.

[Construction of IPS-Mode Liquid-Crystal Cell]

On one glass substrate, electrodes were disposed so that the distancebetween the adjacent electrodes could be 20 μm, and a polyimide filmserving as an alignment film was disposed on it, and this was rubbed. Apolyimide film was disposed on one surface of another glass substrateprepared separately, and rubbed to be an alignment film. The two glasssubstrates were put one upon another in such a manner that theiralignment films could face each other and their distance (gap; d) couldbe 3.9 μm, and stuck together with the rubbing directions of the twoglass substrate kept in parallel to each other; and then a nematicliquid-crystal composition having a refractivity anisotropy (Δn) of0.0769 and having a positive dielectric anisotropy (Δ∈) of 4.5 wassealed up between the two substrates. The liquid-crystal layer had d·Δnof 300 nm.

[Fabrication of Polarizing Plates PL1 to PL6] (Preparation ofThermoplastic-Resin Film F1)

With reference to Production Examples described in “Examples” in JPA No.2006-96960, a thermoplastic-resin film F1 was produced. Concretely, thefilm was produced according to the method mentioned below.

9000 g of methyl methacrylate (MMA), 1000 g of methyl2-(hydroxymethyl)acrylate (MHMA), 10000 g of 4-methyl-2-pentanone(methyl isobutyl ketone, MIBK) and 5 g of n-dodecylmercaptan were fedinto a 30-liter reactor equipped with a stirrer, a temperature sensor, acondenser tube and a nitrogen-introducing duct, and with introducingnitrogen thereinto, this was heated up to 105° C., and when this becamerefluxed, 5.0 g of a polymerization initiator, tertiarybutyl-peroxyisopropyl carbonate (Akzo Chemical's trade name, KayacarbonBic-7) was added thereto and simultaneously with dropwise adding asolution comprising 100 g of tertiary butyl-peroxyisopropyl carbonateand 230 g of MIBK thereto, taking 4 hours, this was subjected tosolution polymerization under reflux (at about 105 to 120° C.), andfurther ripened for 4 hours.

30 g of stearyl phosphate/distearyl phosphate mixture (Sakai Chemical'strade name, Phoslex A-18) was added to the obtained polymer solution,and this was subjected to ring-closing condensation under reflux (atabout 90 to 120° C.) for 5 hours. Next, the polymer solution obtained asa result of the above ring-closing condensation was introduced into avented twin-screw extruder (φ=29.75 mm, L/D=30) having a barreltemperature of 260° C., running at a revolution of 100 rpm and under areduced pressure of from 13.3 to 400 hPa (10 to 300 mmHg), and havingone rear vent and 4 fore vents at a feeding rate of 2.0 kg/hr in termsof the resin amount, and in the extruder, this was further subjected toring-closing condensation with degassing, and extruded out to givetransparent pellets (1A).

The obtained pellets (1A) were analyzed for various physical propertiesthereof according to the method described in JPA No. 2006-96960, andthese were identified as the pellets 1A produced according to Examplesin JPA No. 2006-96960.

Using a 20 mmφ twin-screw extruder, the pellets (1A) obtained inProduction Example 1 were melt-extruded through the coat hunger-typeT-die thereof having a width of 150 mm, thereby producing a film F1having a thickness of about 100 μm. The film F1 was as follows:

Re(630)=0.6 nm,

Rth(630)=−1.7 nm,

|Re(400)−Re(700)=0.1 nm, and

|Rth(400)−Rth(700)|=1.0 nm;

and the film satisfied the above formulae (I) and (II). In addition, thefilm F1 was as follows:

|Re{50}−Re{25}|=1 nm,

|Rth{50}−Rth{25}|=2 nm,

|Re[80]−Re[10]|=0 nm, and

|Rth[80]−Rth[10]|=0.5 nm;

and the film satisfied all the above formulae (III) to (VI).

(Preparation of ZRF Film F2)

A commercially-available cellulose acetate film (ZRF80s, byFUJIFILM—hereinafter this is referred to as “ZRF film”) was used as apolymer film F2. The film F2 was as follows:

Re(630)=1 nm,

Rth(630)=−7 nm,

|Re(400)−Re(700)|=2 nm, and

|Rth(400)−Rth(700)|=15 nm;

and the film was as follows:

|Re{50}−Re{25}|=3 nm,

|Rth{50}−Rth{25}|=10 nm,

|Re[80]−Re[10]|=0.3 nm, and

|Rth[80]−Rth[10]|=16 nm.

(Preparation of TAC Film F3)

A commercially-available cellulose acetate film (Fujitac TD80UF, byFUJIFILM—hereinafter this is referred to as “TAC film”) was used as apolymer film F3. The film F3 was as follows:

Re(630)=1 nm,

Rth(630)=38 nm,

|Re(400)−Re(700)|=0.8 nm, and

|Rth(400)−Rth(700)|=20 nm;

(Polarizing Film)

A stretched polyvinyl alcohol film was processed to adsorb iodine, andthis was used a polarizing film.

(Fabrication of Polarizing Plate PL1)

An isocyanate-based adhesive was applied to the surface ofThermoplastic-resin film F1, and a PVA-based adhesive was applied to thesurface of the TAC film F3; and the polarizing film was sandwichedbetween these films and laminated in a mode of wet lamination withextruding out the superfluous adhesive with a pressure roller. Next,this was heated and dried to produce a polarizing plate.

(Fabrication of Polarizing Plate PL2)

A PVA-based adhesive was applied to the surface of the ZRF film F2, anda PVA-based adhesive was applied to the surface of the TAC film F3; andthe polarizing film was sandwiched between these films and formed into apolarizing plate in the same manner as above.

(Fabrication of Polarizing Plate PL3)

A PVA-based adhesive was applied to the surfaces of the two TAC filmsF3; and the polarizing film was sandwiched between these films andformed into a polarizing plate in the same manner as above.

[Construction of IPS-Mode Liquid-Crystal Display Device]

A liquid-crystal display device having the same constitution as in FIG.1 was constructed. Concretely, this was constructed according to themethod mentioned below.

A panel-side polarizing plate PLa and a back-side polarizing plate PLbwere stuck to the surface and the back of the IPS-mode liquid-crystalcell produced in the above, as in FIG. 1 showing various combinations ofpolarizing plates, thereby constructing liquid-crystal display devicesLCD1 to LCD6. The polarizing plates PL1 and PL2 were so disposed thatthe liquid-crystal cell-side protective film thereof could beThermoplastic-resin film F1 or ZRF film.

[Evaluation]

Thus constructed, the liquid-crystal display devices LCD1 to LCD6 wereevaluated as follows:

The liquid-crystal display devices were left at a temperature of 25° C.and a humidity of 60% for 1 hour, and then at a temperature of 80° C.and a humidity of 10% for 1 hour; and they were tested and evaluated forthe degree of color shift seen in oblique directions in the black stateand for the black brightness at the front (in the normal linedirection). The evaluation standards are shown below. The results aregiven in Table 1.

Color Shift:

AA: Perfectly no color shift.

A: No color shift.

B: Some color shift was seen but on the acceptable level.

C: Color shift was seen.

Front Black Brightness:

AA: Perfectly no light leakage in the front, and no CR reduction.

A: No light leakage in the front, and no CR reduction.

B: Some light leakage, but little CR reduction.

C: Noticeable light leakage in the front with CR reduction.

TABLE 1 Polarizing Polarizing Plate at Plate at Evaluation DisplayingBacklight Front Side Side Color Black LCD PLa PLb Shift Brightness LCD1PL1 PL1 AA AA LCD2 PL2 PL1 AA A LCD3 PL3 PL1 AA B LCD4 PL1 PL2 B A LCD5PL2 PL2 B B LCD6 PL3 PL3 C C

Using a 20 mmφ twin-screw extruder, the pellets (1A) were melt-extrudedthrough the coat hunger-type T-die having a width of 150 mm, withchanging the thickness in melt extrusion, the temperature, the humidityand the stretching condition, thereby producing Thermoplastic-resinfilms F10 to F34 having the optical characteristics shown in thefollowing Table.

Using triacetyl cellulose in a known casting method, comparativeTriacetyl cellulose films F50 to F53 having the optical characteristicsshown in the following Table were produced with changing the thickness,the temperature, the humidity and the stretching condition thereof.

TABLE 2 Variation Variation in in Retardation Retardation depending ondepending Retardation Temperature on Humidity Re(630) Rth(630) ΔRe*1ΔRth*2 Re*3 Rth*4 Re*5 Rth*6 Film No. (nm) (nm) (nm) (nm) (nm) (nm) (nm)(nm) 10 −8 −23 −3 15 −1 7 1 9 11 −8 −12 −3 15 0 3 0 −3 12 −8 −2 −3 15 −1−4 3 2 13 −8 6 −3 15 1 5 −1 8 14 −8 21 −3 15 3 1 −4 0 15 −3 −23 −3 15 26 0 −1 16 −3 −12 −3 15 2 −4 2 −7 17 −3 −2 −3 15 −3 −8 4 1 18 −3 6 −3 151 3 3 6 19 −3 21 −3 15 0 0 −1 −4 20 0.5 −23 −3 15 3 2 2 −8 21 0.5 −12 −315 −1 9 −3 3 22 0.5 −2 −3 15 −4 −3 1 −4 23 0.5 6 −3 15 0 −4 0 0 24 0.521 −3 15 2 8 −2 3 25 4 −23 −3 15 4 0 −3 0 26 4 −12 −3 15 4 −1 0 2 27 4−2 −3 15 0 −7 1 9 28 4 6 −3 15 −2 3 2 7 29 4 21 −3 15 −3 4 −1 3 30 9 −23−3 15 0 −2 −2 −4 31 9 −12 −3 15 1 −5 −1 5 32 9 −2 −3 15 −3 −9 1 3 33 9 6−3 15 −1 5 3 5 34 9 21 −3 15 −2 4 1 4 50 −8 −30 −3 15 −1 7 1 9 51 −8 −23−3 50 −1 7 1 9 52 −20 −23 −3 15 −1 20 1 9 53 −8 −23 −15 15 −1 7 15 20*1|Re(400)-Re(700)| *2|Rth(400)-Rth(700)| *3|Re{50}-Re{25}|*4|Rth{50}-Rth{25}| *5|Re[80]-Re[10]| *6|Rth[80]-Rth[10]|

Polarizing plates PL10 to PL34 were fabricated in the same manner asthat for the polarizing plate PL1, for which, however, the abovethermoplastic-resin films, Thermoplastic-resin film F10 to F34,respectively, were used in place of Thermoplastic-resin film F1.

Polarizing plates PL50 to PL53 were fabricated in the same manner asthat for the polarizing plate PL2, for which, however, the abovetriacetyl cellulose films, Triacetyl cellulose films F50 to F53,respectively, were used in place of the TAC film F3.

Two of the polarizing plates PL10 to PL34 and PL50 to PL53 were used,and liquid-crystal display devices having the same constitution as inFIG. 1 were constructed. Concretely, as the panel-side polarizing platePLa and the back-side polarizing plate PLb, the same polarizing plateswere stuck to the surface and the back of the IPS-mode liquid-crystalcell produced in the above, thereby constructing liquid-crystal displaydevices LCD10 to LCD34 and LCD50 to LCD53. The polarizing plates were sodisposed that the liquid-crystal cell-side protective film thereof couldbe each of the thermoplastic-resin films, Thermoplastic-resin films F10to F34, or each of triacetyl cellulose films F50 to F53.

Thus constructed, the liquid-crystal display devices were evaluated inthe same manner as above. The results are shown in the following Table.

TABLE 3 Evaluation Color Front Black LCD No. PLa PLb Shift BrightnessLCD10 PL10 PL10 A A LCD11 PL11 PL11 AA A LCD12 PL12 PL12 AA A LCD13 PL13PL13 AA A LCD14 PL14 PL14 A A LCD15 PL15 PL15 A AA LCD16 PL16 PL16 AA AALCD17 PL17 PL17 AA AA LCD18 PL18 PL18 AA AA LCD19 PL19 PL19 A AA LCD20PL20 PL20 A AA LCD21 PL21 PL21 AA AA LCD22 PL22 PL22 AA AA LCD23 PL23PL23 AA AA LCD24 PL24 PL24 A AA LCD25 PL25 PL25 A AA LCD26 PL26 PL26 AAAA LCD27 PL27 PL27 AA AA LCD28 PL28 PL28 AA AA LCD29 PL29 PL29 A AALCD30 PL30 PL30 A A LCD31 PL31 PL31 AA A LCD32 PL32 PL32 AA A LCD33 PL33PL33 AA A LCD34 PL34 PL34 A A LCD50 PL50 PL50 C A LCD51 PL51 PL51 C ALCD52 PL52 PL52 C C LCD53 PL53 PL53 C A

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide aliquid-crystal display device, in particular an IPS-mode liquid-crystaldisplay device, that is free from a problem of display performancefluctuation to be caused by temperature- or humidity-change.

It is also possible to provide a liquid-crystal display device, inparticular an IPS-mode liquid-crystal display device, that is free fromproblems of color shift in oblique directions and front contrastreduction to occur depending on the environment humidity andtemperature.

1. A liquid-crystal display device comprising: a liquid-crystal cellwhich comprises: a pair of substrates disposed to face each other havingan electrode on at least one of them, the electrode capable of formingan electric field containing a component running in parallel to thesubstrate, and a liquid-crystal layer, of which alignment is controlled,disposed between the pair of substrates; and a pair of polarizing platesdisposed to sandwich the liquid-crystal cell therebetween, wherein thethickness of the liquid-crystal layer is controlled by any of polymerbeads, glass beads fibers and resinous columnar spacers, and the productof the thickness d (μm) of the liquid-crystal layer and the refractiveanisotropy Δn thereof, Δn·d is from 0.2 to 1.2 μm, wherein at least oneof the pair of polarizing plates comprises a polarizing element and athermoplastic-resin film which comprises a lactone ring-having polymeras a major ingredient and satisfies the following formulas (I) and (II),wherein the lactone ring-having polymer has a repetitive structure unitto be constructed by polymerization of at least one selected from(meth)acrylates, hydroxyl group-containing monomers, unsaturatedcarboxylic acids and monomers of the following formula (2):−3≦Re(630)≦4, and −12≦Rth(630)≦6  (I)|Re(400)−Re(700)|≦10, and |Rth(400)−Rth(700)|≦35  (II) wherein Re(λ)means retardation (nm) in plane at a wavelength λ nm; and Rth(λ) meansretardation (nm) along the thickness direction at a wavelength λ nm:

wherein R⁴ represents a hydrogen atom or a methyl group; X represents ahydrogen atom, an alkyl group having from 1 to 20 carbon atoms, an arylgroup, an acetate group, a cyano group, a group —CO—R⁵ or a group—CO—O—R⁶, wherein R⁵ and R⁶ each represents a hydrogen atom or anorganic residue having from 1 to 20 carbon atoms.
 2. The liquid-crystaldisplay device of claim 1, wherein a polarizing plate disposed at thebacklight side, at least, is said polarizing plate comprising thethermoplastic-resin film.
 3. The liquid-crystal display device of claim1, wherein a polarizing plate disposed at the displaying plane side, atleast, is said polarizing plate comprising the thermoplastic-resin film.4. The liquid-crystal display device of claim 1, wherein both ofpolarizing plates disposed at the backlight side and the displayingplane side are said polarizing plates comprising the thermoplastic-resinfilm.
 5. The liquid-crystal display device of claim 1, wherein Re{T} andRth{T} (T means the temperature (° C.) at which the data is measured) ofthe thermoplastic-resin film at a wavelength of 550 nm satisfy thefollowing formulas (III) and (IV):|Re{50}−Re{25}|<5 nm,  (III)|Rth{50}−Rth{25}|<10 nm.  (IV)
 6. The liquid-crystal display device ofclaim 5, wherein Re{T} and Rth{T} (T means the temperature (° C.) atwhich the data is measured) of the thermoplastic-resin film at awavelength of 550 nm satisfy the following formulas (III) and (IV):|Re{50}−Re{25}|<5 nm,  (III)|Rth{50}−Rth{25}|<10 nm.  (IV)
 7. The liquid-crystal display device ofclaim 1, wherein Re[H] and Rth[H] (H means the relative humidity (%) atwhich the data is measured) of the thermoplastic-resin film at awavelength of 550 nm satisfy the following formulas (V) and (VI):|Re[80]−Re[10]|<5 nm,  (V)|Rth[80]−Rth[10]|<10 nm.  (VI)
 8. The liquid-crystal display device ofclaim 7, wherein Re[H] and Rth[H] (H means the relative humidity (%) atwhich the data is measured) of the thermoplastic-resin film at awavelength of 550 nm satisfy. −3 nm≦Re[80]−Re[10]≦4 nm and −7nm≦Re[80]−Re[10]≦9 nm.
 9. The liquid-crystal display device of claim 1,wherein the lactone ring-having polymer in the thermoplastic-resin filmis from 50 to 100% by mass.
 10. The liquid-crystal display device ofclaim 2, wherein the lactone ring-having polymer in thethermoplastic-resin film is from 50 to 100 by mass.
 11. Theliquid-crystal display device of claim 3, wherein the lactonering-having polymer in the thermoplastic-resin film is from 50 to 100%by mass.
 12. The liquid-crystal display device of claim 1, wherein thelactone ring-having polymer has a weight-average molecular weight offrom 1,000 to 2,000,000.
 13. The liquid-crystal display device of claim2, wherein the lactone ring-having polymer has a weight-averagemolecular weight of from 1,000 to 2,000,000.
 14. The liquid-crystaldisplay device of claim 3, wherein the lactone ring-having polymer has aweight-average molecular weight of from 1,000 to 2,000,000.
 15. Theliquid-crystal display device of claim 1, wherein the lactonering-having polymer has a lactone ring structure of the followingformula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.
 16. The liquid-crystal displaydevice of claim 2, wherein the lactone ring-having polymer has a lactonering structure of the following formula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.
 17. The liquid-crystal displaydevice of claim 3, wherein the lactone ring-having polymer has a lactonering structure of the following formula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.
 18. The liquid-crystal displaydevice of claim 4, wherein the lactone ring-having polymer has a lactonering structure of the following formula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.
 19. The liquid-crystal displaydevice of claim 9, wherein the lactone ring-having polymer has a lactonering structure of the following formula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.
 20. The liquid-crystal displaydevice of claim 12, wherein the lactone ring-having polymer has alactone ring structure of the following formula (1):

wherein R¹, R² and R³ each independently represent a hydrogen atom, oran organic residue having from 1 to 20 carbon atoms, and the organicresidue may contain an oxygen atom.